It is very important for airport control towers to known not only the compass direction of the wind on the landing strips, but also the "wind shear", meaning whether the wind has a downward component or an upward component, and the angle of that component. When the wind is blowing other than strictly parallel to the ground surface, it is essential for pilots of incoming and outgoing aircraft, as well as control tower personnel, to know the angle of the inclination.
Heretofore, no reliable apparatus has been devised for determining this wind shear.